An innovative approach to disentangling the effect of management and environment on tree cover and density of protected areas in African savanna

Abstract

In protected areas of the African savanna tree cover, structure and species composition are influenced by a combination of many different variables. These include complex and multi-scaled interplay of environmental factors such as water and nutrient availability, fire, herbivory and, when occurring, direct human disturbance. In this study, we conducted a comprehensive and comparative analysis of the spatial variability of tree cover and density in three neighboring Southern African National Parks (Kruger, Limpopo, and Gonarezhou) characterized by similar environmental conditions but different management plans. We sampled 3382 plots of 0.5 ha across the three parks using an innovative methodology defined as augmented visual interpretation, based on a free and open source software. This software, named Collect Earth, allows access to very high spatial and temporal resolution imagery archives. Spatial variability of tree cover and density was analyzed comparing the three parks and the two bioclimatic regions (semiarid and dry subhumid) characterizing them. The effect of relevant environmental variables such as edaphic factors, precipitation and fire frequency was also assessed. Kruger National Park is characterized by the lowest values of tree cover and density among the three Parks. Contrary to what was expected and the general trend of Southern Africa, the dry subhumid zone showed lower values of tree cover and density than the semiarid zone. Such variability is hypothesized to be related to the different managements of the three parks within the general environmental template characterizing the African savanna as well as differences in tree species composition between the two climatic zones.